A key component of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
Perpendicular magnetic recording has become the standard for magnetic data recording. Such recording systems use a magnetic media having high magnetic anisotropy grains. Often a capping layer is applied over the high magnetic anisotropy grains, followed by a protective overcoat such as carbon. The cap layer provides a strong in-plain magnetic coupling between the magnetic grains. This cap layer improves the writeability and thermal stability of the media, enabling writing to the high magnetic anisotropy grains under the cap layer. The cap layer also improves the surface roughness and corrosion robustness.
However currently available cap layers present challenges. Since the cap layer is deposited on top of the well separated oxide grains, the initial growth layer of the cap up to 2 nm is also well separated and does not provide enough exchange coupling between grains. This initial 2 nm of the cap layer has been referred to as the dead layer, because the cap layer growth is separated in this region. The magnetic coercivity Hc of the media goes up in this dead region, then starts to go down with more exchange coupling as the thickness of the cap layer increases. For this reason cap layers have had to be at 4 nm thick or thicker to get sufficient exchange coupling. A thicker cap increases the spacing between the head and the high magnetic anisotropy grains as well as spacing between the head and the soft magnetic under-layer of the media, which decreases performance of the disk drive system. This increased spacing decreases the resolution of the media and is not suitable for future high density magnetic recording.
One approach that has been proposed to overcome this challenge is to use a higher saturation magnetization (Ms) alloy for the cap layer. Such media can provide better exchange coupling with thinner total cap thickness, but this type of cap layer also increases the coupling between the cap and thin oxide layer that forms a non-magnetic boundary between magnetic grains. Stronger coupling between the cap and the oxide layer reduces the write assist effectiveness of the capping layer, so that such systems do not work well.